Page 107 - SST Class 06

LONGITUDE AND TIME China. This country stretches from 75°E to 135°E.
If every 15 degrees are taken for the local time, it
We know that the Earth rotates on its axis and would have as many as 5 local times.
takes about 24 hours in one rotation. As 360
longitudes are drawn on the Earth, we can say that Similar is the case for India. It stretches from 68°E
the Sun faces these longitudes, one by one, once to 97°E, so it should have at least three local
in a day. Now, the longitude facing the Sun times, which would create a lot of confusion. In
directly has the noon or the time of 12 o’clock at order to alleviate this confusion, a standard time is
noon. As the Earth rotates from west to east, it adopted. In India, the longitude of 82½°E is
appears that the Sun is going round from east to treated as the standard meridian. The local time of
west. It also means that when a particular this longitude is taken as the standard time for the
longitude is having noon, the longitudes situated whole country. This time is known as the Indian
to its east have already experienced noon while Standard Time (IST). The Indian Standard Time is
those in the west will have noon in the time to 5 hours and 30 minutes ahead of the Greenwich
come. As the Earth rotates 360 degrees in 24 Mean Time (GMT). It means when it is 12 o’clock
hours, it rotates about 15 degrees in one hour or 1 noon at Greenwich, it will be 5:30 pm in India.
degree in every 4 minutes. When a cricket match starts at 10 am in London,
we can view it live on television at 3:30 pm.
Thus, if it is 12 o’clock noon at 100°E now, it will Similarly, if a Twenty-20 match starts in India at
be 12 o’clock noon at 115°E after one hour from
10 am, the people in London can listen to its live
now and it was 12 o’clock noon at 85°E one hour commentary at 4:30 am onwards.
ago from now. It also follows that the longitude
Just Think!
just opposite it will have 12 o’clock midnight.
Now, let’s take the example with the Prime
Meridian in view, which is marked 0°. When it is If your friend in England wants to talk to you in
12 o’clock noon here, it will be 1 o’clock afternoon the morning at 5:30 am GMT, when should you ring
at 15°E, 2 o’clock afternoon at 30°E and so on. him up as per the IST?
Similarly, it will be 11 o’clock forenoon at 15°W
and 10 o’clock forenoon at 30°W and so on. A F G H A N I S T A NF G H A N I S T A N
A
JAMMU
JAMMU
& &
KASHMIRKASHMIR
Ladakh
Ladakh
S
Leh
Leh
SRINAGARRINAGAR
Info Bits
Info Bits HIMACHALMACHAL C C H I N AH I N A 36°
HI
PRADESH
PRADESH
SHIMLALA
SHIM TIBET
TIBET
PUNJAB
PUNJAB
CHANDIGARHGARH
The exact time that the Earth takes to rotate once on P A K I S T A NA K I S T A N CHANDI HARY NA ANA UTTARAKHANDTARAKHAND 32°
UT
DEHRADUN
DEHRADUN
P
R NACHA
its axis is 23 hours 56 minutes and 4.091 seconds. HARYA DEL N E P SIKKIMSIKKIM A U ACH L AL
DELHIHI
PR DESH
A UN
A ESH
R
AD
N E P A
A L L PR
IT
UTTARTAR
R A J A S T H A NA J A S T H A N UT GANGTOKOK BHUTANAN ITANAGARANAGAR 28°
R
GANGT
BHUT
PRADESH
JAIPUR PRADESH ASSAM
JAIPUR
ASSAM
Local Time LUCKNOW DISPUR NAGALAND
NAGALAND
DISPUR
KOHIMA
KOHIMA
LUCKNOW
PATNANA SHILLONGILLONG
PAT
SH
MANIPUR
B
MEGHALA
B I H A RI H A R MEGHALAYAYA MANIPUR
IMPH
IMPHALAL
By local time of a place on a certain longitude is GANDHINAGAR ARKHAND BANGLADESH AIZAWLWL 24°
BANGLADESH
ND
AGARTALATALA
AGAR
GANDHINAGAR
AIZA
WEST TRIPURATRIPURA
G U J A R A TU J A R A T BHOP MADHYAMADHYA G RH JH WEST MIZORAM
MIZORAM
G
GA
BENGAL
BHOPALAL
RANC
RANCHIHI
meant that it is exact 12 o’clock noon when the PRADESHPRADESH HHATTIS ARH JHARKHA BENGAL
KOLKA
KOLKATATA
Daman CHHATTIS
C
Daman
DIU
Sun shines just overhead. All places on this (D&D) (D&D) M M A H A R A S H T R AA H A R A S H T R A RAIPURR O O D I S H AD I S H A MY 20°
DIU
(D&D) D &NHD &NH
RAIPU
MYANMARANMAR
(D&D) SILVASSASILVASSA
BHUBANESWARUBANESWAR
BH
longitude will have the same time. MUMBAI
MUMBAI
HYDERABAD
HYDERABAD
O
A A R A B I A NR A B I A N S E AE A A B B AYAY O FF B B E N G A LE N G A L 16°
S
G NA
A R N A T A K A
Standard Time TELA N ANA E H SH
ELA GA
N
T
NDHRA PRADES
P PANAJIANAJI K A R N A T A K ANDHRA PRAD
There are many countries which cover many GOA K A 12°
GOA
longitudes. If each of its places starts to observe L BENGALURU D U CHENNAIHENNAI
C
BENGALURU
I L N A D U
the local time, it would create a lot of confusion. (IN LAKSHAD K E T A M I L N A (I (INDI POR 8°
PORT BLAIRT BLAIR
When a train travels from one longitude to (INDIA) AKSHADWEEP KA KAVARATTIVARATTI K E R A L T A M ND A) IA) ANDAMAN AND NICOBAR ISLANDS SEA
ANDAMAN
ANDAMAN
DIA)
SEA
R A L A
WEEP
another, it would be difficult to make a timetable. THIRUV A Gulf of of
THIRUVANANTHAPURAMANANTHAPURAM
Gulf
Mannar
Mannar
KANYAKUMARIAKUMARI
KANY
Same will be the case in case of television and S R
S R I I
ANDAMAN AND NICOBAR ISLANDS
L A N K
L A N K A A
I N D I A NN D I A N O O C E A NC E A N
I
64° 68° 72° 76° 80° 84° 88° 92°
radio programmes. Let us take the example of
Latitudes, longitudes and IST Meridian at 82½ºE
Globe : The Model of the Earth
107